1. Field of the Invention
The present invention relates to an improved prepupillary lens which may be surgically implanted into the posterior chamber of a human eye and more particularly to a method for securing the lens within the chamber.
2. Description of the Prior Art
In the prior art prepupillary lenses have been used in an operation for surgically implanting a lens on the iris of a human eye. Cornelius D. Binkhorst, M.D., who has performed this operation since 1958, has used a two loop lens and a four-loop lens. He has described both of these lenses in an article entitled "The Iridocapsular (Two-loop) Lens and the Iris-clip (Four-loop) Lens in Pseudophakia", which he wrote for the 1973 September-October edition of Transactions of the American Academy of Opthalmology and Otolaryngology. These lenses are made from a plastic material, polymethyl methacrylate, which is commonly used to make contact lenses. The lenses are in the shape of a plano convex lens and have a diameter of 5.0 millimeters and a central thickness of from 0.5 millimeters to 0.6 millimeters depending on the required lens strength.
U.S. Pat. No. 3,994,027, entitled Prepupillary Lens for Implanting in a Human Eye, issued to Ronald P. Jensen and James Fetz on Nov. 30, 1976 teaches a two-loop lens which has its loops buried in the posterior chamber of the human eye, but which rests within the anterior chamber of the human eye. The difficulty with this position of the two-loop lens is that this is not the normal position of the original lens. The placement of the lens in the anterior chamber of the human eye is unnatural and creates a problem in the restoration of accurate binocular vision. Further the lens in the anterior chamber is not adjacent to the hyloid membrane for supporting the vitreous humor thereby making instances of forward displacement of the vitreous humor and retinal detachment more likely to occur.
Another difficulty with this type of lens is that it is formed out of a plastic material which transmits infrared light and ultraviolet light to the retina.
The prior art also teaches an artificial intraocular lens for implantation in the posterior chamber of an eye which includes an optical zone portion fabricated of transparent material and shaped similar to a natural lens and a plurality of prongs attached to the optical zone portion near its periphery. The prongs protrude forwardly therefrom for insertion through the iris of the eye to hold and position the lens therein. The difficulty with this lens is that it is affixed to the iris of the eye and therefore it is not rigidly anchored thereby allowing the lens to move with eye movement. Subsequently, the iris may erode and the fixation of the lens may be lost. It would be far better to anchor the intraocular lens within the posterior chamber to the capsular membrane which is a very firm, non-viable tissue and which provides firm, secure and permanent fixation of the lens.
Another prior art device teaches a lens for implantation in the eye which has a resilient flange that is sutured to the ciliary muscle of the eye to position and to retain the lens in the same position as the original lens. This lens irritates the ciliary body so that inflammation is likely to occur. The fixation of the lens to the ciliary body is not only a difficult surgical procedure, but also does not provide a firm, secure or permanent fixation of the lens.
U.S. Pat. No. 3,913,148, entitled Intraocular Lens Apparatus, issued to Ernst W. Potthast on Oct. 21, 1975, U.S. Pat. No. 3,991,426, entitled Posterior Chamber Artificial Intraocular Lens with Retaining Means and Instruments for Use Therewith, issued to Leonard Flom and Kenneth J. Rodgerson Nov. 16, 1976, and U.S. Pat. No. 4,014,049, entitled Artificial Intraocular Lens and Supporting System Therefor, all teach intraocular lenses that are positioned in the posterior chamber of the eye and that are fixated to the iris of the eye.
U.S. Pat. No. 4,079,470, entitled Artificial Intraocular Lens, issued to Emil W. Deeg and David A. La Marre on Mar. 2, 1978, teaches a chemically durable biologically inert optical implant lens formed of a low density natural or synthetic crystal, such as Corundum, Sapphire, Ruby, Sircon, Strontium, Diamond or Anatase. Special sprectral transmittances desired for specific color vision effects and ultraviolet protection may be accomplished by synthetic crystals. These metal ions absorb the ultraviolet rays within the intraocular lens.
The inventor refers to an application having Ser. No. 862,534, filed on Dec. 20, 1977 by Michael E. Fourney and Ronald P. Jensen, entitled An Infra-red Reflective Coating for Protecting Eye of Cataract Patients (now abandoned), and hereby incorporates the material by reference thereto.
Another prior art intraocular lens teaches a chemically durable, inert optical implant lens formed out of a glass composition which has spectral transmission characteristics simulating those of human crystalline lenses and which specifically absorbs ultraviolet light. This implant lens is too heavy for a human eye, because it is basically formed out of glass and has a density in the range of 2.46 to 3.05 grams per cubic centimeters. The plastic lenses have a density of approximately 1.0 grams per cubic centimeters. It is therefore desirable to obtain the advantage of both the low density of the plastic lenses and the infrared transmission characteristic of this particular glass lens.
The inventor has studied the various methods of making implant lenses and has come to the conclusion that it is better to reflect the infrared radiation and the ultraviolet radiation than it is to absorb them because those lenses which absorb the infrared radiation and ultraviolet radiation have a tendency to lower the transmission of the visible radiation in the absorption process.